Gynoecium (/ɡaɪˈniːsi.əm,dʒɪˈniːʃi.əm/; from Ancient Greek γυνή (gunḗ) 'woman, female' and οἶκος (oîkos) 'house';pl.:gynoecia) is most commonly used as a collective term for the parts of aflower that produceovules and ultimately develop into thefruit andseeds. The gynoecium is the innermostwhorl of a flower; it consists of (one or more)pistils and is typically surrounded by thepollen-producingreproductive organs, thestamens, collectively called theandroecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing femalegametes (i.e.egg cells), the gynoecium producesmegaspores, each of which develops into a femalegametophyte which then produces egg cells.
The term gynoecium is also used by botanists to refer to a cluster ofarchegonia and any associated modified leaves or stems present on a gametophyte shoot inmosses,liverworts, andhornworts. The corresponding terms for the male parts of those plants are clusters ofantheridia within the androecium. Flowers that bear a gynoecium but no stamens are calledpistillate orcarpellate. Flowers lacking a gynoecium are called staminate.
The gynoecium is often referred to as female because it gives rise to female (egg-producing) gametophytes; however, strictly speakingsporophytes do not have a sex, only gametophytes do.[1][page needed] Gynoecium development and arrangement is important in systematic research and identification ofangiosperms, but can be the most challenging of the floral parts to interpret.[2]
Unlike (most)animals,plants grow new organs afterembryogenesis, including new roots, leaves, and flowers.[3] In the flowering plants, the gynoecium develops in the central region of the flower as a carpel or in groups of fused carpels.[4] After fertilization, the gynoecium develops into a fruit that provides protection and nutrition for the developing seeds, and often aids in their dispersal.[5] The gynoecium has several specialized tissues.[6] The tissues of the gynoecium develop from genetic and hormonal interactions along three-major axes.[7][8] These tissue arise frommeristems that produce cells that differentiate into the different tissues that produce the parts of the gynoecium including the pistil, carpels, ovary, and ovules; the carpel margin meristem (arising from the carpelprimordium) produces theovules, ovary septum, and the transmitting track, and plays a role in fusing the apical margins of carpels.[9]
The gynoecium may consist of one or more separate pistils. A pistil typically consists of an expanded basal portion called anovary, an elongated section called astyle and anapical structure called astigma that receives pollen.
The word "pistil" comes fromLatinpistillum meaningpestle. A sterile pistil in a male flower is referred to as apistillode.
The pistils of a flower are considered to be composed of one or morecarpels.[note 1] A carpel is the female reproductive part of the flower—usually composed of thestyle, andstigma (sometimes having its individualovary, and sometimes connecting to a shared basal ovary) —and usually interpreted as modified leaves that bear structures calledovules, inside which egg cells ultimately form. A pistil may consist of one carpel (with its ovary, style and stigma); or it may comprise several carpels joined together to form a single ovary, the whole unit called a pistil. The gynoecium may present as one or more uni-carpellate pistils or as one multi-carpellate pistil. The number of carpels is denoted by terms such astricarpellate (three carpels).
Carpels are thought to bephylogenetically derived from ovule-bearing leaves or leaf homologues (megasporophylls), which evolved to form a closed structure containing the ovules. This structure is typically rolled and fused along the margin.
Although many flowers satisfy the above definition of a carpel, there are also flowers that do not have carpels because in these flowers the ovule(s), although enclosed, are borne directly on the floral apex.[12][17] Therefore, the carpel has been redefined as an appendage that encloses ovule(s) and may or may not bear them.[18][19][20] However, the most unobjectionable definition of the carpel is simply that of an appendage that encloses an ovule or ovules.[21]
If a gynoecium has a single carpel, it is calledmonocarpous. If a gynoecium has multiple, distinct (free, unfused) carpels, it isapocarpous. If a gynoecium has multiple carpels "fused" into a single structure, it issyncarpous. A syncarpous gynoecium can sometimes appear very much like a monocarpous gynoecium.
| Gynoecium composition | Carpel terminology | Pistil terminology | Examples |
|---|---|---|---|
| Single carpel | Monocarpous (unicarpellate) gynoecium | A pistil (simple) | Avocado (Persea sp.), most legumes (Fabaceae) |
| Multiple distinct ("unfused") carpels | Apocarpous (choricarpous) gynoecium | Pistils (simple) | Strawberry (Fragaria sp.),Buttercup (Ranunculus sp.) |
| Multiple connate ("fused") carpels | Syncarpous gynoecium | A pistil (compound) | Tulip (Tulipa sp.), most flowers |
The degree of connation ("fusion") in a syncarpous gynoecium can vary. The carpels may be "fused" only at their bases, but retain separate styles and stigmas. The carpels may be "fused" entirely, except for retaining separate stigmas. Sometimes (e.g.,Apocynaceae) carpels are fused by their styles or stigmas but possess distinct ovaries. In a syncarpous gynoecium, the "fused" ovaries of the constituent carpels may be referred to collectively as a single compound ovary. It can be a challenge to determine how many carpels fused to form a syncarpous gynoecium. If the styles and stigmas are distinct, they can usually be counted to determine the number of carpels. Within the compound ovary, the carpels may have distinct locules divided by walls calledsepta. If a syncarpous gynoecium has a single style and stigma and a single locule in the ovary, it may be necessary to examine how the ovules are attached. Each carpel will usually have a distinct line of placentation where the ovules are attached.
Pistils begin as small primordia on a floral apical meristem, forming later than, and closer to the (floral) apex than sepal, petal and stamen primordia.Morphological andmolecular studies of pistil ontogeny reveal that carpels are most likely homologous to leaves.[citation needed]
A carpel has a similar function to amegasporophyll, but typically includes a stigma, and is fused, with ovules enclosed in the enlarged lower portion, the ovary.[22]
In somebasal angiosperm lineages,Degeneriaceae andWinteraceae, a carpel begins as a shallow cup where the ovules develop with laminar placentation, on the upper surface of the carpel. The carpel eventually forms a folded, leaf-like structure, not fully sealed at its margins. No style exists, but a broad stigmatic crest along the margin allows pollen tubes access along the surface and between hairs at the margins.[22]
Two kinds of fusion have been distinguished: postgenital fusion that can be observed during the development of flowers, and congenital fusion that cannot be observed i.e., fusions that occurred during phylogeny. But it is very difficult to distinguish fusion and non-fusion processes in the evolution of flowering plants. Some processes that have been considered congenital (phylogenetic) fusions appear to be non-fusion processes such as, for example, the de novo formation of intercalary growth in a ring zone at or below the base of primordia.[23][24][25] Therefore, "it is now increasingly acknowledged that the term 'fusion,' as applied to phylogeny (as in 'congenital fusion') is ill-advised."[26]
Basal angiosperm groups tend to have carpels arranged spirally around a conical or dome-shapedreceptacle. In later lineages, carpels tend to be inwhorls.
The relationship of the other flower parts to the gynoecium can be an important systematic and taxonomic character. In some flowers, the stamens, petals, and sepals are often said to be "fused" into a "floral tube" orhypanthium. However, as Leins & Erbar (2010) pointed out, "the classical view that the wall of the inferior ovary results from the "congenital" fusion of dorsal carpel flanks and thefloral axis does not correspond to the ontogenetic processes that can actually be observed. All that can be seen is an intercalary growth in a broad circular zone that changes the shape of the floral axis (receptacle)."[25] And what happened during evolution is not a phylogenetic fusion but the formation of a unitary intercalary meristem. Evolutionary developmental biology investigates such developmental processes that arise or change during evolution.
If the hypanthium is absent, the flower ishypogynous, and the stamens, petals, and sepals are all attached to the receptacle below the gynoecium. Hypogynous flowers are often referred to as having asuperior ovary. This is the typical arrangement in most flowers.
If the hypanthium is present up to the base of the style(s), the flower isepigynous. In an epigynous flower, the stamens, petals, and sepals are attached to the hypanthium at the top of the ovary or, occasionally, the hypanthium may extend beyond the top of the ovary. Epigynous flowers are often referred to as having aninferior ovary. Plant families with epigynous flowers includeorchids,asters, andevening primroses.
Between these two extremes areperigynous flowers, in which a hypanthium is present, but is either free from the gynoecium (in which case it may appear to be a cup or tube surrounding the gynoecium) or connected partly to the gynoecium (with the stamens, petals, and sepals attached to the hypanthium part of the way up the ovary). Perigynous flowers are often referred to as having ahalf-inferior ovary (or, sometimes,partially inferior orhalf-superior). This arrangement is particularly frequent in therose family andsaxifrages.
Occasionally, the gynoecium is born on a stalk, called thegynophore, as inIsomeris arborea.
Within the ovary, each ovule is born by a placenta or arises as a continuation of the floral apex. The placentas often occur in distinct lines called lines ofplacentation. In monocarpous or apocarpous gynoecia, there is typically a single line of placentation in each ovary. In syncarpous gynoecia, the lines of placentation can be regularly spaced along the wall of the ovary (parietal placentation), or near the center of the ovary. In the latter case, separate terms are used depending on whether or not the ovary is divided into separate locules. If the ovary is divided, with the ovules born on a line of placentation at the inner angle of each locule, this isaxile placentation. An ovary withfree central placentation, on the other hand, consists of a single compartment without septae and the ovules are attached to a central column that arises directly from the floral apex (axis). In some cases a single ovule is attached to the bottom or top of the locule (basal orapical placentation, respectively).
In flowering plants, theovule (from Latinovulum meaning small egg) is a complex structure born inside ovaries. The ovule initially consists of a stalked, integumentedmegasporangium (also called thenucellus). Typically, one cell in the megasporangium undergoesmeiosis resulting in one to four megaspores. These develop into a megagametophyte (often called the embryo sac) within the ovule. The megagametophyte typically develops a small number of cells, including two special cells, an egg cell and a binucleate central cell, which are thegametes involved indouble fertilization. The central cell, once fertilized by a sperm cell from the pollen becomes the first cell of theendosperm, and the egg cell once fertilized become thezygote that develops into theembryo. The gap in the integuments through which the pollen tube enters to deliver sperm to the egg is called themicropyle. The stalk attaching the ovule to the placenta is called the funiculus.
Stigmas can vary from long and slender to globe-shaped to feathery. The stigma is the receptive tip of the carpel(s), which receives pollen atpollination and on which the pollen graingerminates. The stigma is adapted to catch and trap pollen, either by combining pollen of visiting insects or by various hairs, flaps, or sculpturings.[27]
The style and stigma of the flower are involved in most types ofself incompatibility reactions. Self-incompatibility, if present, preventsfertilization by pollen from the same plant or from genetically similar plants, and ensures outcrossing.
The primitive development of carpels, as seen in such groups of plants asTasmannia andDegeneria, lack styles and the stigmatic surface is produced along the carpels margins.[28]
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